Clinical research in strabismus currently suffers from a paucity of validated outcome measures. In this application we propose to develop and validate a series of outcome measures to be used in future randomized clinical trials in strabismus and, in the course of developing these measures, we will answer a number of important clinical questions 1) To further develop and continue to validate a new scoring system for diplopia - and determine whether improvement in a diplopia score reflects the perception of improvement by the patient 2) To further develop and continue to validate scoring systems for control and stability of intermittent exotropia - and determine the natural history of intermittent exotropia, describing the proportion of children with intermittent exotropia that show improvement, remain the same, or worsen, over several years follow-up 3) To further test and validate measures of distance stereopsis - and determine whether distance stereoacuity is degraded by intermittent exotropia and other conditions where the distance deviation is greater than the near deviation, and determine whether distance stereoacuity will be predictive of which children with intermittent exotropia will decompensate. The outcome measures developed and tested in the present protocol will then be used in future randomized clinical trials in strabismus. The long-term goal of this research is to define the patients with strabismus who would benefit most from intervention, to define the best treatments for specific types of strabismus, and to reduce unnecessary or futile eye surgery. Ultimately this research will result in better quality of life for patients with strabismus.